英文:
class java.util.ArrayList cannot be cast to class org.springframework.util.MultiValueMap
问题
[{"name": "巴布亚新几内亚","value": "PG"},{"name": "美国","value": "US"},...]
public Map<String, Object> getCountryNameCodeList() {String[] countryCodes = Locale.getISOCountries();Map<String, Object> list = new HashMap<>();for (String countryCode : countryCodes) {Locale obj = new Locale("", countryCode);list.put(obj.getDisplayCountry(), obj.getCountry());}return list;}@GetMapping("shipping_countries")public ResponseEntity<List<Map<String, String>>> getShippingCountries() {Map<String, Object> list = countriesService.getCountryNameCodeList();List<Map<String, String>> countries = new ArrayList<>();for (Map.Entry<String, Object> entry : list.entrySet()) {Map<String, String> country = new HashMap<>();country.put("name", entry.getKey());country.put("value", entry.getValue().toString());countries.add(country);}return new ResponseEntity<>(countries, HttpStatus.OK);}
出现错误的原因是在返回ResponseEntity时，您尝试将dtos（类型为ArrayList）转换为MultiValueMap，这是不正确的。我已经根据您的代码对其进行了修复，现在应该能够获得您所期望的 JSON 响应，并且不会再出现错误。
英文:
I want to generate a JSON response which includes inner JSON Objects. I tried this:
public Map<String, Object> getCountryNameCodeList() {String[] countryCodes = Locale.getISOCountries();Map<String, Object> list = new HashMap<>();for (String countryCode : countryCodes) {Locale obj = new Locale("", countryCode);list.put(obj.getDisplayCountry().toString(), obj.getCountry());}return list;}
Rest Api:
@GetMapping("shipping_countries")public ResponseEntity<Set<Map.Entry<String, Object>>> getShippingCountries() {Map<String, Object> list = countriesService.getCountryNameCodeList();List<KeyValueDTO> dtos = new ArrayList();for(Map.Entry<String, Object> value: list.entrySet()) {KeyValueDTO dto = new KeyValueDTO();dto.setKey(value.getKey());dto.setValue(value.getValue().toString());dtos.add(dto);}return new ResponseEntity<Set<Map.Entry<String, Object>>>((MultiValueMap<String, String>) dtos, HttpStatus.OK);}
I want to get this response:
[{name: "Papua New Guinea",value: "PG"},{name: "Unites States",value: "US"},....]
But I get this error:
class java.util.ArrayList cannot be cast to class org.springframework.util.MultiValueMap (java.util.ArrayList is in module java.base of loader 'bootstrap'; org.springframework.util.MultiValueMap is in unnamed module of loader org.springframework.boot.loader.LaunchedURLClassLoader @6267c3bb)
How I can fix this issue?
答案1
得分: 1
似乎您正在将一个列表 List<KeyValueDTO> 强制转换为一个多映射 (MultiValueMap<String, String>)。它们是完全不同的类型 - 列表不是映射。因此，在您的帖子中出现了异常。尝试在不进行转换的情况下返回该值。
英文:
It seems you are typecasting List<KeyValueDTO> a list into (MultiValueMap<String, String>) a multimap. They are totally different types - a list is not a map. Hence, the exception in your post. Try to return the value without the cast.
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